The present invention relates to a system for providing navigational information to a user. The increasing use of portable appliances, such as wireless telephones and personal digital assistants (PDAs), has led to widespread use of such devices during travel. If and when such travelers become lost or otherwise need navigational directions, it would be very convenient and useful to receive such directions through their wireless devices.
A number of navigational systems are available or under development. Systems available over the internet allow users to receive directions from a starting point to a destination, and to receive an accompanying map. Such systems, however, do not provide real-time directions; once the user is on the road, the user cannot receive clarification or updates to the directions.
As used herein, “real-time” refers to an approximate correspondence with the actual time in which events are taking place. For instance, a user seeking real-time directions from the corner of Main Street and First Street seeks them at the approximate time the user is actually at Main Street and First Street.
As used herein, “navigational information” broadly refers to information relating to geographic navigation. In many instances, the navigational information comprises navigational directions to the user, instructing the user, for instance, which way and how far to go to reach a destination. In other instances, navigational information may refer to other navigation-related information, such as the user's current, past, or future location(s) or other information relating to the user's navigation.
Other systems are becoming popular for use in automobiles. Such systems often provide a graphical map or directions to the user. In some cases, these system employ satellite-based global positioning system (GPS) to identify the location of the vehicle. Examples of such systems are disclosed in U.S. Pat. Nos. 5,938,720; 5,928,307; 5,922,042; 5,912,635; 5,910,177; 5,904,728; 5,902,350; and 6,055,478, each of which is incorporated herein by reference. These systems, however, generally require specialized equipment in the vehicle, such as specialized input/output apparatus, graphical displays, a map database, or processor. Such equipment is expensive and cumbersome for the user, especially in those situations where the user is walking, changing vehicles, or otherwise away from the vehicle in which the equipment is installed. Therefore, there is a need in the art to provide navigation systems in personal handheld devices.
In addition, there is a need for wireless mobile devices, and mobile telephones in particular, to have location-identifying capability. Recent government regulations have highlighted the need for wireless carriers to provide such capabilities and services.
There are several technical obstacles that stand in the way of the incorporation of navigational capabilities in handheld devices for providing turn-by-turn real-time navigation services. One such obstacle is the amount of geographic data needed to provide reasonably detailed navigational information. Small handheld devices include, for example, cellular phones, personal digital assistants, or computers. The amount of embedded memory in such devices is limited and thus they are not suited for storage of large amounts of geographic information. Geographic information is usually stored in a geographic mapping database stored on a CD-ROM, hard-disk drive device or other large capacity storage medium.
Another obstacle is the lack of information processing power in small devices, such as those mentioned above. For example, the information processing power of a wireless telephone is typically provided by an embedded microprocessor with limited memory. While the information processing power of embedded microprocessors is generally increasing, such processors are still not suitable for processor intensive real-time navigational tasks.
An additional obstacle is the insufficient location accuracy provided by current technology. Initial sources of inaccuracy of the GPS based systems, for example, may, be imposed by the U.S. Department of Defense through Selective Availability (S/A), while other sources of error are due to atmospheric and timing errors limiting the accuracy of a single GPS receiver to +/−50 meters. Methods exist that can be used to enhance the location accuracy to about +/−5 meters. Such methods include Enhanced GPS systems (i.e., SnapTrack) and network based system (i.e., Truepoint). These methods use a known position, such as a survey control point, as a reference point to correct the GPS position error. These methods of correcting GPS positions are referred to as Differential GPS or DGPS. The DGPS corrections can be applied to the GPS data in real-time using data telemetry (radio modems). Toward expanding the use of DGPS, the United States and Canadian Coast Guard are establishing a series of radio beacons to transmit the DGPS corrections for accurate navigation along the Great Lakes, the Mississippi River and tributaries, the Gulf Coast, and the Eastern and Western coasts of North America. However, such radio beacons are not available to consumers traveling in most inland locations. For the remainder of this application, the terms “GPS” and “DGPS” will be used interchangeably, unless indicated otherwise.
Navigational systems are difficult to develop further because the desired accuracy depends on the particular application. For example, if the user is driving in a downtown area with closely spaced streets, a GPS location with accuracy within, for instance, +/−50 meters is not adequate to give turn-by-turn directions. In this context, GPS location information is thus considered ambiguous and inappropriate for practical navigation. In other situations, providing a GPS location within +/−50 meters is, however, perfectly adequate for navigation purposes. For example, if a user is driving on a highway in a remote area without any nearby exits, the GPS location is sufficient for calculating further navigation directions. Thus, in such a situation, the GPS location is not ambiguous.
Current automobile GPS navigation systems make use of other sensors, such as accelerometers, speedometers, etc. plus sophisticated filtering technology to improve the accuracy of a navigational system (see, e.g., U.S. Pat. No. 5,912,635, previously incorporated by reference for all purposes). In addition, many automobile-based navigational systems use map-aiding technology as well. However, for a navigational system implemented using handheld devices, such as cellular telephones, it is undesirable to require the handheld device to be connected to external sensors, especially when the device is used while walking.
Other obstacles confront navigational systems designed for use when walking. U.S. Pat. No. 6,029,069, which is incorporated herein by reference, is an example of such a system. Such systems are generally limited by the user's communication device. For instance, it is difficult for a user to enter detailed information over a wireless telephone in a format that is useful for the central processor, especially if the user is engaged in other activities such as driving a vehicle. These systems are also susceptible to imperfections of the underlying service; for instance, establishing or maintaining a connection over the wireless network(s) can be difficult. Also, the rate of transfer of information over wireless networks can be extremely limiting.
Accordingly, it would be desirable to provide a navigational system and service which improves upon the inadequacies of prior systems.